The effects of grain geometry on waterflooding and viscous fingering in micro-fractures and porous media from a lattice Boltzmann method study

The study of fluid fronts formed in porous media is important for enhanced oil recovery. The purposes of this study are to simulate waterflooding and to investigate influential factors on the fluid front movement through a micro-fracture and through simple porous media with different grain geometries. This study used the Shan-Chen form of the Lattice Boltzmann Method (LBM). An increase in the velocity is found to result in viscous fingering, whereas an increase in the wettability of the displacing fluid and the dynamic viscosity ratio creates a piston form of the fluid front. In porous media with the same porosities, various geometries act differently as obstacles against fluid flow from the inlet to the outlet. By enlarging the cross-sectional area of grains in the fluid paths and making them more tortuous, narrower and more twisted films of viscous fingering are formed. The sweep efficiency was also determined under various conditions: with a fixed capillary number, neutral wettability and different viscosity ratios; and with a fixed capillary number, viscosity ratio of (1/3) and wet or non-wet conditions. In all cases, the best sweep efficiency was obtained with grains of diamond geometry. Generally, the least sweep efficiency occurs with grains of star geometry. Simulation results verified the strength and accuracy of LBM predictions.